Progress in building methods was slow until the Industrial Revolution ushered in an age when tremendous improvements (steel, iron, cement etc.) and machinery (powered, at first, by steam and coal) made possible a quantum jump in the complexity and quality of structures. Modern materials and equipment made possible the deeper and stronger foundations that were required for skyscrapers and bridges, etc. In the past century progress in improvement of materials and machinery has not matched the revolution brought about by the age of iron and steel and coal and steam, but has resulted instead in a great many refinements by comparison. For the future, the depletion of natural resources including agricultural land and fossil fuels will require structures whose form and location will be conditional by these depletions. Deeper excavations and higher superstructures will challenge the foundation engineer to provide larger and more difficult substructures.